Radiation image read-out apparatus including selective stimulating ray reflection preventing means

ABSTRACT

A radiation image read-out apparatus comprises an optical system for scanning a stimulable phosphor sheet carrying a radiation image stored therein by stimulating rays, a light guide member for guiding light emitted by the stimulable phosphor sheet upon exposure to stimulating rays, a light guiding mirror for reflecting the emitted light to the light guide member, and a photoelectric converter for detecting the light guided by the light guide member. The light guiding mirror is provided with a reflection plane which reflects the light emitted by the stimulable phosphor sheet and which does not reflect stimulating rays. Or, a filter for absorbing the stimulating rays reflected by the stimulable phosphor sheet and transmitting the light emitted by the stimulable phosphor sheet is positioned between the scanned portion of the stimulable phosphor sheet and the light guiding mirror.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a radiation image read-out apparatus in aradiation image recording and reproducing system using a stimulablephosphor sheet.

2. Description of the Prior Art

A radiation image recording and reproducing system using a stimulablephosphor sheet is disclosed, for example, in U.S. Pat. Nos. 4,258,264and 4,315,318, and Japanese Unexamined Patent Publication No.56(1981)-11395. The system was also announced at meetings of theradiation society, in "Nikkan Kogyo Shinbun" (Daily IndustrialNewspaper), June 23, 1981 edition, page 16, and elsewhere, and attractedattention in various fields.

The aforesaid radiation image recording and reproducing system iscapable of providing various radiation images useful for viewing,particularly for diagnostic purposes, which could not be obtained byconventional radiography using a silver halide photographic material.Moreover, the radiation image recording and reproducing system canfurther provide improved diagnostic effects when combined with anup-to-date medical image recording technique such as computed tomography(CT) or introduction of radioisotope into the human body. Therefore, thesystem is very effective for viewing purposes, particularly for medicaldiagnosis.

The aforesaid radiation image recording and reproducing system generallycarries out the steps of (i) recording (storing a radiation image in astimulable phosphor sheet), (ii) read-out (converting the stored imageinto an image signal, and sometimes storing the read-out image signal ona conventional medium such as magnetic tape), and (iii) reproducing(converting the image signal into a visible image, i.e. displaying thevisible image on a display device such as a cathode ray tube (CRT) orpermanently recording the visible image on a recording medium such asphotographic film). The present invention is concerned with the read-outstep in the aforesaid radiation image recording and reproducing system.

FIG. 1 is a schematic view showing an example of a radiation imageread-out apparatus employed in the aforesaid radiation image recordingand reproducing system.

In the apparatus of FIG. 1, a laser beam 1a of a predetermined intensityis emitted as stimulating rays from a laser beam source 1 to agalvanometer mirror 2. The laser beam 1a is deflected by thegalvanometer mirror 2 to form a laser beam 1b impinging upon astimulable phosphor sheet 3 positioned below the galvanometer mirror 2so that the stimulable phosphor sheet 3 is scanned by the laser beam 1bin the main scanning direction, i.e. in the width direction of the sheet3 as indicated by the arrow A. While the laser beam 1b impinges upon thestimulable phosphor sheet 3, the sheet 3 is conveyed in the sub-scanningdirection as indicated by the arrow B, for example, by an endless beltdevice 9. Therefore, scanning in the main scanning direction is repeatedat an angle approximately normal to the sub-scanning direction, and thewhole surface of the stimulable phosphor sheet 3 is two-dimensionallyscanned by the laser beam 1b. As the stimulable phosphor sheet 3 isscanned by the laser beam 1b, the portion of the sheet 3 exposed to thelaser beam 1b emits light having an intensity proportional to the storedradiation energy. The light emitted by the stimulable phosphor sheet 3enters a transparent light guide member 4 from its light input face 4apositioned close to the sheet 3 in parallel to the main scanning line. Alight guiding mirror 10 having a plane parallel to the main scanningdirection is positioned to stand face to face with the light input face4a. The light guiding mirror 10 reflects the light, which is emitted bythe stimulable phosphor sheet 3 towards the light guiding mirror 10, tothe light input face 4a, thereby improving the light guiding efficiencyof the light guide member 4.

The light guide member 4 has a flat-shaped front end portion 4bpositioned close to the stimulable phosphor sheet 3 and is shapedgradually into a cylindrical shape towards the rear end side to form anapproximately cylindrical rear end portion 4c which is closely contactedwith a photomultiplier 5. The light emitted by the stimulable phosphorsheet 3 upon stimulation thereof and entering the light guide member 4from its light input face 4a is guided inside of the light guide member4 up to the rear end portion 4c, and received by the photomultiplier 5.A filter (not shown) transmitting the light emitted by the stimulablephosphor sheet 3 and absorbing the stimulating rays is positionedbetween the rear end portion 4c of the light guide member 4 and thephotomultiplier 5, thereby intercepting the stimulating rays enteringthe light guide member 4 by being reflected by the stimulable phosphorsheet 3 after impinging thereupon. Therefore, only the light emitted bythe stimulable phosphor sheet 3 is guided to the photomultiplier 5. Thusthe light emitted by the stimulable phosphor sheet 3 in proportion tothe radiation energy stored therein is detected and converted into anelectric image signal by the photomultiplier 5. The electric imagesignal thus obtained is sent to an image processing circuit 6 andprocessed therein. The electric image signal thus processed is thenreproduced into a visible image and displayed, for example, on a CRT 7,or is stored in a magnetic tape 8.

However, in the radiation image read-out apparatus arranged as describedabove, a problem arises when the stimulable phosphor sheet 3 is scannedby the laser beam (stimulating rays) 1b. Namely, the laser beam 1bimpinging upon the stimulable phosphor sheet 3 is reflected by the sheet3 to the light input face 4a and the light guiding mirror 10, and isfurther reflected by the light input face 4a and the light guidingmirror 10 to portions of the sheet 3 that have not yet been scanned,thereby stimulating the non-scanned portion and causing it to emitlight. When light is emitted by the non-scanned portion of thestimulable phosphor sheet 3 outside of the scanned portion thereof, thelight is guided by the light guide member 4 together with the lightemitted by the scanned portion of the sheet 3, and is processed as if itwere image information from the scanned portion. Therefore, thereproduced image thus obtained becomes incorrect.

FIG. 2 is an enlarged perspective view showing the section near thepoint 3a of FIG. 1. The aforesaid problem will further be described withreference to FIG. 2 by using as an example the laser beam 1c at a giveninstant in the scanning by the laser beam 1b in FIG. 1 as an example.The point 3a on the stimulable phosphor sheet 3 exposed to the laserbeam 1c emits light in proportion to the radiation energy stored thereinupon stimulation by the laser beam 1c. At the same time, the laser beam1c impinging upon the point 3a is partially reflected and scattered bythe point 3a. A part of the laser beam reflected and scattered isfurther reflected by the light input face 4a of the light guide member 4and the reflection plane of the light guiding mirror 10 as indicated, byway of example, by arrows 11a, 11b, and 11c, and impinges uponnon-scanned portions of the stimulable phosphor sheet 3 outside of thepoint 3a, thereby stimulating the non-scanned portions and causing themto emit light.

SUMMARY OF THE INVENTION

The primary object of the present invention is to provide a radiationimage read-out apparatus in which stimulating rays impinging upon astimulable phosphor sheet and reflected thereby toward the reflectionplane of the light guiding mirror are not reflected by the reflectionplane.

Another object of the present invention is to provide a radiation imageread-out apparatus realizing a reproduced visible image of high imagequality.

The present invention provides a radiation image read-out apparatusincluding a scanning optical system for scanning a stimulable phosphorsheet carrying a radiation image stored therein by stimulating rays, alight guide member having a light input face positioned in the vicinityof a portion of said stimulable phosphor sheet scanned by saidstimulating rays, said light guide member guiding light, which isemitted by said stimulable phosphor sheet in proportion to the storedradiation energy when said stimulable phosphor sheet is scanned by saidstimulating rays, from said light input face, a light guiding mirrorpositioned in the vicinity of said light input face and said portion ofsaid stimulable phosphor sheet scanned by said stimulating rays, saidlight guiding mirror reflecting the light emitted by said scannedportion to said light input face, and a photoelectric converter forreceiving the light guided by said light guide member andphotoelectrically converting it into an electric signal,

wherein the improvement comprises the provision of:

(i) a stimulating ray reflection preventing means positioned betweensaid portion of said stimulable phosphor sheet scanned by saidstimulating rays and said light guiding mirror, and

(ii) a means for preventing transmission of said stimulating rays andtransmitting the light emitted by said stimulable phosphor sheet inproportion to the stored radiation energy, said means positioned betweensaid light guiding mirror and said photoelectric converter.

In the present invention, the stimulating ray reflection preventingmeans may be constituted as a reflection plane of the light guidingmirror which reflects the light emitted by the stimulable phosphor sheetand which does not reflect the stimulating rays, and the means forpreventing transmission of stimulating rays and transmitting the lightemitted by the stimulable phosphor sheet may be a filter positioned atthe photoelectric converter for selectively transmitting the lightemitted by the stimulable phosphor sheet. Alternatively, the stimulatingray reflection preventing means and the means for preventingtransmission of stimulating rays and transmitting the light emitted bythe stimulable phosphor sheet may be constituted by a single filter forabsorbing the stimulating rays and transmitting the light emitted by thestimulable phosphor sheet. In this case, the filter is positionedbetween the portion of the stimulable phosphor sheet scanned by thestimulating rays and the light guiding mirror. In addition to thefilter, another filter of the same type may also be positioned betweenthe portion of the stimulable phosphor sheet scanned by the stimulatingrays and the light input face of the light guide member.

In the present invention, since the stimulating ray reflectionpreventing means is positioned between the scanned portion of thestimulable phosphor sheet and the light guiding mirror, no light isemitted by the non-scanned portion of the stimulable phosphor sheetoutside of the scanned portion thereof, and it is possible to obtain areproduced visible image of high image quality.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view showing the conventional radiation imageread-out apparatus,

FIG. 2 is an enlarged perspective view showing the section near thepoint 3a of FIG. 1,

FIG. 3 is an enlarged sectional view showing a part of an embodiment ofthe radiation image read-out apparatus in accordance with the presentinvention, which corresponds to a sectional view taken along line II--IIof FIG. 1,

FIG. 4 is a plan view showing another embodiment of the radiaiton imageread-out apparatus in accordance with the present invention,

FIG. 5 is an enlarged side view showing a part of the apparatus of FIG.4, which is taken in the direction as indicated by the arrow D of FIG.4, and

FIGS. 6A to 6D are side views showing further embodiments of theradiation image read-out apparatus in accordance with the presentinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will hereinbelow be described in further detailwith reference to the accompanying drawings.

The embodiments of the radiation image read-out apparatus in accordancewith the present invention as shown in FIGS. 3 to 6D have aconfiguration similar to the configuration of the conventional apparatusshown in FIG. 1 except that in FIG. 3 a stimulating ray reflectionpreventing film is overlaid on the light input face of the light guidemember and the light guiding mirror is provided with a reflection planewhich reflects the light emitted by the stimulable phosphor sheet andwhich does not reflect the stimulating rays, and that in FIGS. 4 to 6D afilter for absorbing the stimulating rays and transmitting the lightemitted by the stimulable phosphor sheet is positioned between theportion of the stimulable phosphor sheet scanned by the stimulating raysand the light guiding mirror. Therefore, in FIGS. 3 to 6D, similarelements are numbered with the same reference numerals with respect toFIG. 1.

Referring to FIG. 3, the light input face 4a of the light guide member 4positioned along the portion of the stimulable phosphor sheet 3 scannedby the stimulating rays 1b is provided with a stimulating ray reflectionpreventing film 13, and a light guiding mirror 10 having a reflectionplane 10a is positioned along the scanned portion of the stimulablephosphor sheet so that the reflection plane 10a stands face to face withthe light input face 4a of the light guide member 4. The stimulating rayreflection preventing film 13 is used for preventing the stimulatingrays from being reflected by the light input face 4a, thereby furtherimproving the image quality of the reproduced visible image. However,the stimulating ray reflection preventing film 13 need not necessarilybe provided.

The light guiding mirror 10 having the reflection plane 10a should besuch that it reflects the light emitted by the stimulable phosphor sheet3 and impinging upon the reflection plane 10a and that, owing totransmission, absorption or the like, it does not reflect thestimulating rays. In order to fabricate the light guiding mirror 10 sothat it exhibits such optical property, a surface of metal aluminium maybe subjected to alumite coloration treatment, thereby forming a coloredalumite film as the reflection plane 10a. In this case, the surface ofmetal aluminium is subjected to anodic oxidation, and at the same timecolored by a dye which reflects the light emitted by the stimulablephosphor sheet 3 and which absorbs the stimulating rays. In this manner,the colored alumite film having the aforesaid optical property is formedas the reflection plane 10a on the surface of metal aluminium. Or, thelight guiding mirror 10 may be fabricated as a dichroic mirror byoverlaying a dichroic coating as the reflection plane 10a on the surfaceof a substrate of glass, a plastic material, or the like. Of course, inthis case, the dichroic coating overlaid on the substrate surface mustexhibit the optical property of reflecting the light emitted by thestimulable phosphor sheet 3 and transmitting the stimulating rays. Thestimulating rays of a comparatively long wavelength (e.g. 633 nm)impinging upon the reflection plane 10a are absorbed by the reflectionplane 10a (in the case of the colored alumite film) or are transmittedtherethrough (in the case of the dichroic coating). Therefore, thestimulating rays are not reflected by the light guiding mirror 10, andonly the light having a comparatively short wavelength (e.g. 400 nm)emitted by the stimulable phosphor sheet 3 is reflected by the lightguiding mirror 10.

The stimulating ray reflection preventing film 13 should be such that itprevents reflection of the stimulating rays 1b and reflection of thelight emitted by the stimulable phosphor sheet 3, thereby efficientlyguiding the light emitted by the stimulable phosphor sheet 3 into thelight guide member 4. As the stimulating ray reflection preventing film13 exhibiting such optical property, it is possible to use, for example,a deposited thin film of a material exhibiting a refractive indexsmaller than that of the material of the light guide member 4. In thecase where the deposited thin film is provided, reflection of thestimulating rays 1b becomes minimum when the optical thickness of thedeposited thin film is a quarter of the wavelength of the stimulatingrays 1b. Reflection of the stimulating rays 1b is completely eliminatedwhen the condition n1=√n2 holds between the refractive index n1 of thedeposited thin film material and the refractive index n2 of the lightguide member material. When the light guide member 4 is fabricated of aplastic material or glass, the material of the deposited thin filmpositioned on the light input face of the light guide member 4 may beMgF₂, CaF₂, cryolite, or the like. The deposited thin film preventsreflection of the stimulating rays 1b and the light emitted by thestimulable phosphor sheet 3. Therefore, the light emitted by thestimulable phosphor sheet 3 is efficiently guided into the light guidemember 4. The stimulating rays 1b prevented from reflection by thedeposited thin film and guided into the light guide member 4 areabsorbed and eliminated by the filter positioned between the light guidemember 4 and the photomultiplier 5. The light emitted by the stimulablephosphor sheet 3 and allowed to enter the light guide member 4 since itis not reflected by the deposited thin film passes through the filterand is received by the photomultiplier 5.

The light guiding mirror 10 is not limited to the one as describedabove, and may be of any type insofar as it reflects the light emittedby the stimulable phosphor sheet 3 and does not reflect the stimulatingrays.

FIGS. 4 and 5 show another embodiment of the radiation image read-outapparatus in accordance with the present invention. In this embodiment,a plate-like filter 15 for absorbing the stimulating rays 1d reflectedby the stimulable phosphor sheet 3 and transmitting the light emitted bythe stimulable phosphor sheet 3 is positioned between the position 3a,where the stimulating rays 1b impinge upon the sheet 3, and a lightguiding mirror 14 for reflecting the light emitted by the stimulablephosphor sheet 3 to the light guiding mirror 4a of the light guidemember 4.

The filter 15 may, for example, be a wavelength selection transmittingfilter which absorbs the reflected stimulating rays 1d and transmits thelight emitted by the stimulable phosphor sheet 3 on the basis of thedifference in the wavelength distribution therebetween. As the filter15, it is possible to use, for example, filter NO. B-380 supplied byHoya Garasu K.K. when the wavelength of the reflected stimulating rays1d is 633 nm and the wavelength of the light emitted by the stimulablephosphor sheet 3 is 390 nm. Of course, absorption of the reflectedstimulating rays 1d and transmission of the light emitted by thestimulable phosphor sheet 3, which are effected by the filter 15, neednot necessarily be perfect.

The filter 15 may be closely contacted with the whole front end face ofthe light guiding mirror 14 including a curved reflection plane as shownin FIG. 6A, or may be closely contacted with only the curved reflectionplane as shown in FIG. 6B. Also, the filter may be positioned in a flatplate form near the curved reflection plane as shown in FIG. 6C, or maybe closely contacted with the whole surface of a straight reflectionplane as shown in FIG. 6D.

In the embodiments of FIGS. 4 to 6D, the filter 15 is positioned tostand face to face with the light guiding mirror 14 or is closelycontacted therewith approximately over the entire length of the lightguiding mirror 14 so that all the stimulating rays 1d reflected in sucha direction as to impinge upon the reflection plane of the light guidingmirror 14 are absorbed by the filter 15. However, the filter 15 may alsobe positioned only at a part of the light guiding mirror 14.

Also, some filters may exhibit a relatively low transmittance of thelight emitted by the stimulable phosphor sheet or slight reflection ofthe emitted light from the filter surface. When such filters are used,the efficiency of guiding the light emitted by the stimulable phosphorsheet is decreased more or less. In such a case, it is possible toposition the filter 15 vertically moveably, for example, in theembodiment of FIG. 4. Normally, the filter 15 is maintained in the upperposition to avoid interference with the light emitted by the stimulablephosphor sheet 3. When decrease in the flare phenomenon caused by thereflected stimulating rays is more important than the light guidingefficiency, for example, when a slight difference in contrast should bediscriminated as in the case where a tumor image near a portion of thestimulable phosphor sheet exposed to a high radiation dose outside ofthe object is diagnosed or minute calcification is diagnosed inmammography, the filter 15 is moved down to absorb the reflectedstimulating rays.

We claim:
 1. A radiation image read-out apparatus including a scanningoptical system for scanning a stimulable phosphor sheet carrying aradiation image stored therein by stimulating rays, a light guide memberhaving a light input face positioned in the vicinity of a portion ofsaid stimulable phosphor sheet scanned by said stimulating rays, saidlight guide member guiding light, which is emitted by said stimulablephosphor sheet in proportion to the stored radiation energy when saidstimulable phosphor sheet is scanned by said stimulating rays, from saidlight input face, a light guiding mirror positioned outside said lightguide member in the vicinity of said light input face and said portionof said stimulable phosphor sheet scanned by said stimulating rays, saidlight guiding mirror reflecting the light emitted by said scannedportion to said light input face, and a photoelectric converter forreceiving the light guided by said light guide member andphotoelectrically converting it into an electric signal,wherein theimprovement comprises(i) a stimulating ray reflection preventing meanspositioned between said portion of said stimulable phosphor sheetscanned by said stimulating rays and said light guiding mirror, and (ii)a means for preventing transmission of said stimulating rays andtransmitting the light emitted by said stimulable phosphor sheet inproportion to the stored radiation energy, said means positioned betweensaid light guiding mirror and said photoelectric converter.
 2. Anapparatus as defined in claim 1 wherein said stimulating ray reflectionpreventing means is constituted as a reflection plane of said lightguiding mirror which reflects the light emitted by said stimulablephosphor sheet and which does not reflect said stimulating rays, andsaid means for preventing transmission of said stimulating rays andtransmitting the light emitted by said stimulable phosphor sheet is afilter positioned at said photoelectric converter for selectivelytransmitting the light emitted by said stimulable phosphor sheet.
 3. Anapparatus as defined in claim 2 wherein said reflection plane of saidlight guiding mirror comprises a colored alumite film for reflecting thelight emitted by said stimulable phosphor sheet and absorbing saidstimulating rays.
 4. An apparatus as defined in claim 2 wherein saidreflection plane of said light guiding mirror comprises a dichroiccoating which reflects the light emitted by said stimulable phosphorsheet and which transmits said stimulating rays.
 5. An apparatus asdefined in claim 1, wherein said stimulating ray transmission preventionmeans comprises a stimulating ray reflection preventing film provided onsaid light input face of said light guide member.
 6. An apparatus asdefined in claim 5 wherein said stimulating ray reflection preventingfilm is a deposited thin film of a material exhibiting a refractiveindex smaller than the refractive index of the material of said lightguide member.
 7. An apparatus as defined in claim 6 wherein the opticalthickness of said deposited thin film is a quarter of the wavelength ofsaid stimulating rays.
 8. An apparatus as defined in claim 6 wherein thematerial of said deposited thin film and the material of said lightguide member satisfy the condition n1=√n2 where n1 denotes therefractive index of the material of said deposited thin film and n2denotes the refractive index of the material of said light guide member.9. An apparatus as defined in claim 5 wherein said stimulating rayreflection preventing film also prevents reflection of said lightemitted by said stimulable phosphor sheet.
 10. An apparatus as definedin claim 1 wherein said stimulating ray reflection preventing means andsaid means for preventing transmission of said stimulating rays andtransmitting the light emitted by said stimulable phosphor sheet areconstituted by a first filter for absorbing the stimulating raysreflected by said stimulable phosphor sheet and transmitting said lightemitted by said stimulable phosphor sheet, said first filter beingpositioned between said portion of said stimulable phosphor sheetscanned by said stimulating rays and said light guiding mirror.
 11. Anapparatus as defined in claim 10 wherein said first filter is awavelength selection transmitting filter.
 12. An apparatus as defined inclaim 10 wherein said light guiding mirror has a curved reflectionplane, and said first filter is closely contacted at least with saidcurved reflection plane.
 13. An apparatus as defined in claim 10 whereinsaid light guiding mirror has a curved reflection plane, and said firstfilter is positioned in a flat plate form close to said curvedreflection plane.
 14. An apparatus as defined in claim 10 wherein saidlight guiding mirror has a straight reflection plane, and said firstfilter is closely contacted with the whole surface of said straightreflection plane.
 15. An apparatus as defined in claim 10 wherein, inaddition to said first filter, a second filter of the same type as saidfirst filter is positioned between said portion of said stimulablephosphor sheet scanned by said stimulating rays and said light inputface of said light guide member.